syntax highlighting for all formats supported by "highlight"

The highlight tool can be given any of the supported file extensions
as its -S parameter. This patch replaces the case-switch by extracting
the extension from the supplied file name and passing it to highlight.
However, this requires a shell supporting the ${var##pattern} syntax,
like dash or bash.

Unknown extensions cause a fall-back to plain text using the --force
switch. Error messages are redirected to /dev/null.

A special case maps Makefile and Makefile.* to the "mk" extension.

The total overhead is reduced by calling "exec highlight". No forks are
needed during script execution.

Signed-off-by: Georg Lukas <georg@op-co.de>

filters/syntax-highlighting.sh

@@ -3,6 +3,10 @@
 # tree-view by refering to this file with the source-filter or repo.source-
 # filter options in cgitrc.
 #
+# This script requires a shell supporting the ${var##pattern} syntax.
+# It is supported by at least dash and bash, however busybox environments
+# might have to use an external call to sed instead.
+#
 # Note: the highlight command (http://www.andre-simon.de/) uses css for syntax
 # highlighting, so you'll probably want something like the following included
 # in your css file (generated by highlight 2.4.8 and adapted for cgit):
@@ -20,20 +24,11 @@
 # table.blob .kwc  { color:#000000; font-weight:bold; }
 # table.blob .kwd  { color:#010181; }
 
-case "$1" in
-	*.c)
-		highlight -f -I -X -S c
-		;;
-	*.h)
-		highlight -f -I -X -S c
-		;;
-	*.sh)
-		highlight -f -I -X -S sh
-		;;
-	*.css)
-		highlight -f -I -X -S css
-		;;
-	*)
-		highlight -f -I -X -S txt
-		;;
-esac
+# store filename and extension in local vars
+BASENAME="$1"
+EXTENSION="${BASENAME##*.}"
+
+# map Makefile and Makefile.* to .mk
+[ "${BASENAME%%.*}" == "Makefile" ] && EXTENSION=mk
+
+exec highlight --force -f -I -X -S $EXTENSION 2>/dev/null